Simply put, your life revolves around those activities that stimulate the pleasure centres of your brain. How much you dedicate yourself to your passion is determined by the extent of your pleasure centre stimulation following an action. If your pleasure centres are stimulated following a productive action, you’re lucky. If your pleasure centres are stimulated following a counterproductive action, I’m sorry for your life. If you still don’t know what tickles your pleasure centres, get out and explore.
Start building stuff. It doesn’t have to be world class. You mention Arduino and physical computing. Build something cool with it. Maybe a personal problem perhaps. An example would be – find out a way to make a LED blink via Arduino USB serial whenever you get an IM or even an alert on Quora. This need will take you through learning about using various serial port libraries, writing a listener on Arduino, sniffing a particular port on your computer for IMs and some DOM magic on the browser for events.